1. Field of the Invention
The present invention relates to an imaging apparatus, or more particularly, to an imaging apparatus from which a photographic lens can be separated and in which a main power source is included in a main unit of the imaging apparatus.
2. Description of the Related Art
In the past, connection using a flexible printed-circuit board has generally been adopted in order to electrically connect a lens holding frame with a main unit of an imaging apparatus while absorbing a stroke of the lens holding frame that moves in an optical-axis direction along with a power variation operation or focus operation. For example, an example has been proposed in Japanese Unexamined Utility Model Publication No. 61-206943. This is regarded as a first prior art.
The first prior art is such that entities whose positions change relatively are mutually connected by utilizing elastic deformation of a flexible printed-circuit board, and has such an advantage that an electrical resistance does not differ from that of a normal rigid printed-circuit board.
For placing a flexible printed-circuit board that can be deformed flexibly in a limited space within a lens barrel, it is required to efficiently avoid interference with other members and minimize the space occupied by the flexible printed-circuit board. For this purpose, a countermeasure such as inclusion of a means for controlling the position of a flexible printed-circuit board which moves unitedly with the lens barrel is sometimes taken. Moreover, the flexible printed-circuit board is provided with two or more conduction lines in order to control a focus mechanism and shutter mechanism within a lens holding frame.
Japanese Unexamined Utility Model Publication No. 57-9914 has proposed a technical means in which, when a focus lens driving mechanism to be driven for a focus operation, a shutter driving mechanism, or the like is incorporated in a lens holding frame that moves in an optical-axis direction along with a power variation operation, the motive power of an actuator locked in a main unit of an imaging apparatus is used to control the driving of the mechanism. This shall be regarded as a second prior art.
In other words, the second prior art is such that an actuator fixed to a main unit of an imaging apparatus is driven by a power source locked in the main unit of the imaging apparatus, and the motive power is conveyed to a driving mechanism within a lens holding frame. At this time, motive power conveyance is achieved by a mechanism composed of a lever, a link, a gear (long-span gear in which the length of teeth to be meshed with one another in an optical-axis direction is large), and the like so that the motive power can be conveyed reliably irrespective of a shift of the lens holding frame in the optical-axis direction relative to the main unit of the imaging apparatus.
Using the technical means having the foregoing components, it becomes unnecessary to include an actuator, which drives a driving mechanism within a lens holding frame, in the lens holding frame. The lens holding frame that is a movable member becomes compact and lightweight. Moreover, there are such advantages that it becomes unnecessary to supply electric power used to drive the actuator from a main unit of an imaging apparatus to the lens holding frame, and that therefore the number of electrical connections becomes small or the electrical connections become unnecessary.
Moreover, Japanese Unexamined Utility Model Publication No. 63-90883 has proposed a technique in which a circuit pattern is molded unitedly with a jut formed on a plastic body of an electrical equipment or the like, then the circuit pattern is electrically connected to a circuit pattern on a printed-circuit board, and thus space use efficiency of lines is improved. This shall be regarded as a third prior art.
Furthermore, Japanese Unexamined Utility Model Publication No. 61-206943 has proposed a technical means in which a light emitting device or light receiving device is placed in both a lens barrel, which is inserted into a mount of a camera body and placed so that the lens barrel can be moved freely in an optical-axis direction relative to the mount, and the camera body for the purpose of signal transmission. This shall be regarded as a fourth prior art.
Moreover, Japanese Unexamined Patent Publication No. 62-100744 has disclosed a technical means in which a plurality of segments having two kinds of reflectances; large and small reflectances are placed on a side of a photographic lens opposed to a camera body in order to convey information of the photographic lens to the camera body. This shall be regarded as a fifth prior art.
In this case, light emitting devices are placed in the camera body in association with the segments. Thus, a binary-coded signal corresponding to the large or small reflectance of each segment can be transmitted from the lens to the camera body without the necessity of an electrical connection means.
However, in the first prior art, the flexible printed-circuit board repeats deformation along with the movement of the lens holding frame all the time. An adverse effect of a flare, ghost, or the like, which results from reflection of abaxial rays or the like within the lens barrel, on optical performance is unavoidable.
Connection using a flexible printed-circuit board is intended to absorb the changes in relative position of a movable lens holding frame and a main unit of an imaging apparatus using deformation (bending) of the flexible printed-circuit board. Repeated occurrence of stress on a bend of the flexible printed-circuit board is unavoidable.
For avoiding a drawback such as disconnection deriving from a fatigue failure of a printed-circuit board, it is required to reserve a space of a certain size or larger for the bend and the like. Moreover, since two or more conduction lines are formed on the printed-circuit board, the lateral width of the board becomes large. This becomes an obstruction to realization of a compact design of a lens barrel.
Furthermore, although it is preferable to include a flexible printed-circuit board position control means in order to prevent interference with other members, the inclusion becomes a factor of increasing size and cost.
As mentioned above, while there has been a trend toward a longer stroke of a movement of a lens holding frame due to a higher power of a zoom lens in recent years, if a flexible printed-circuit board is used for electrical connections between the lens holding frame and a main unit of an imaging apparatus, there are many problems to be overcome and difficulties arise.
In the second prior art, although electrical connections between a lens holding frame and a main unit of an imaging apparatus become unnecessary, a mechanical member must be used to convey motive power. The space occupied by the power conveyance mechanical member makes a whole lens barrel large in size.
In particular, if the stroke of the movement of the lens holding frame increases with an increase in power of a zoom lens, problems occur: a coupler must be made larger in order to ensure mechanical coupling between the lens holding frame and the main unit of the imaging apparatus; a dead space within the lens barrel expands; and the accuracy in position control for driving deteriorates.
Moreover, the third prior art has the drawback that it cannot be used as electrical connection means of members that make a relative shift in position.
Furthermore, in the fourth prior art, signal transmission between a lens barrel and camera body is based on communications. An electrical connection means is needed to supply power to the lens barrel. An increase in the stroke of the movement in an optical-axis direction of the lens barrel is unpreferable in terms of space use efficiency.
When the fourth prior art is adapted for a case in which some group of lenses moves in the optical-axis direction inside the lens barrel during, for example, a focus operation in a zoom lens barrel, additional line connections are needed in the lens barrel.
Moreover, the fifth prior art poses no problem as long as information inherent to a photographic lens is transmitted to a camera body. However, for example, when an attempt is made to transmit a state transition of the lens as information to the camera body, the reflectances of segments are requested to be variable. In this case, the segments become considerably expensive.
Supposing all that is requested is identification of the kind of a lens, then no problem occurs. However, if an attempt is made to transmit a large quantity of information for the purpose of controlling focus lens driving or shutter driving, the number of segments and the numbers of associated light emitting devices and light receiving devices increase. This leads to an increase in cost.